1. Field of Invention
The present invention relates to electro-optical devices provided with semiconductor layers formed on substrates, and to electronic equipment using the same. In particular, the present invention relates to an electro-optical device in which each gate-electrode provided on a semiconductor layer extends in the longitudinal direction of a gate so that the ends of the gate electrode are disposed outside the semiconductor layer. The invention also relates to an electronic equipment using the electro-optical device.
2. Description of Related Art
Hitherto, an SOI technology for depositing a thin silicon film on an insulative substance, and forming a semiconductor device on the thin silicon film has been widely studied because the technology contributes to elements having increased speed, reduced power consumption, greater levels of integration, and the like.
An SOI technology is a technology for manufacturing an SOI substrate by bonding monocrystalline-silicon substrates. This technology, generally called a bonding method, is a method for bonding a monocrystalline-silicon substrate with a supporting substrate by using a hydrogen bonding force, reinforcing the bonding force by heat treatment, and grinding and polishing the monocrystalline-silicon substrate; or a method for forming a thin monocrystalline-silicon layer on a supporting substrate by etching. By this method, in which a thin film is made directly from a monocrystalline-silicon substrate, a highly efficient device having superior crystallinity in the thin silicon film is obtainable.
Other methods using the bonding method are known. In one method, a monocrystalline-silicon substrate is doped with hydrogen ion, the monocrystalline-silicon substrate is bonded to a supporting substrate, and a thin silicon layer is separated from a hydrogen-doped region of the monocrystalline-silicon substrate by heat treatment (U.S. Pat. No. 5,374,564). In another method, a monocrystalline-silicon layer is epitaxially grown on a porous surface of a silicon substrate, the silicon substrate is bonded to a supporting substrate, then the silicon substrate is removed, and the porous silicon layer is etched, thereby forming an epitaxial monocrystalline thin silicon film on the supporting substrate (Japanese Unexamined Patent Application Publication No. 4-346418). SOI substrates manufactured by these bonding methods are used for various devices in the same way as conventional bulk semiconductor substrates. A feature of the SOI substrates which is different from that of the conventional bulk substrates is that different types of material can be used for the supporting substrates. Transparent quartz and glass substrates other than conventional silicon substrates can be used. By forming a thin monocrystalline-silicon film on the transparent substrate, a highly efficient transistor element can be provided by using monocrystalline silicon having superior crystallinity for a device which requires light transmissibility, such as a light-transmissive liquid crystal display device.
In a MOSFET (metal oxide semiconductor field effect transistor) element on a conventional silicon substrate, a parasitic MOSFET is prevented from being driven by setting the concentration of impurity in a region under a field oxide film (so-called LOCOS), which separates a MOSFET region, to a concentration higher than that in the well.